1. Field of the Invention
This invention relates to air pallets for frictionless material handling and more particularly to an air pallet of low cost construction which incorporates improved air dispersion means for the air under pressure directed to the plenum chamber.
2. Description of the Prior Art
Air pallets for material handling have come into vogue, as evidenced by U.S. Pat. No. 3,948,344 issuing Apr. 6, 1976, assigned to the same assignee as this application. The present invention is directed to improved air dispersion means which may be incorporated preferably externally of the plenum chamber to facilitate the jacking of air under light pressure internally of the air pallet and within the plenum chamber provided thereby. In the referred to patent, the air pallet permits frictionless movement of a load supported on the support surface. The air pallet constitutes an essentially rigid planar backing surface which could be the load itself with the load uniformly distributed over that surface. The pallet employs a flexible thin sheet which directly underlies the backing surface and directly overlies the fixed support surface. The portion of the flexible thin sheet facing the generally planar fixed support surface is perforated, with the exception of a perimeter portion, to a desired height, to achieve sheet pillowing upon the application of air pressure within the plenum chamber defined by the thin sheet and the backing surface. The provision of air dispersion means is required for the air pallet to insure air flow from a localized inlet or hole within the plenum chamber wall throughout the chamber and to effect jacking of the load and chamber pressurization. The means for controlling pillowing of the chamber is necessary to permit the air pallet to accommodate surface irregularities for both the load support and the backing surface and without sheet ballooning, that is, achieving a spherical shape with resultant tilting and loss of the load carried on the load carrying backing surface.
The air dispersion means provided within the embodiments of the air pallet of our prior patent are formed within the chamber and take the form of spaced projections or strips mounted to the backing surface or to the flexible thin sheet or formed integrally therewith, or by way of a separate planar member such as a cardboard sheet or planar sheet with surface projections thereon. In this fashion, the application of low pressure air to the inlet to the chamber causes air distribution throughout the chamber even though the load applied to the air pallet presses the flexible thin sheet carrying the perforations tightly between the planar backing surface and the load support surface. By the incorporation of the means for controlling pillowing, initially no air is permitted to escape the plenum chamber, but as the load is jacked upwardly, the perforations closest to the perimeter or periphery of the flexible thin sheet are raised from the underlying fixed pallet and load support surface, and the air discharging through the perforations directly escapes therefrom. An air film is set up between the flexible sheet and the fixed support surface, constituting an air cushion to permit the frictionless movement of the pallet and its load relative to that fixed support surface.
The flexible thin sheet may constitute a bag which in turn carries internally a planar member forming the air dispersion means and in fact the load itself may form the rigid backing surface.
Alternatively, the flexible thin sheet may be heat sealed or otherwise bonded about its periphery to a generally rigid, planar backing member such as a cardboard sheet of a size similar to that of the flexible thin sheet carrying the perforations and underlying that backing and load carrying member.